Berlin: The mystery which lasted for more than 60 years over the spread of the worst E coli epidemic has finally come to rest. The highly aggressive strain of E coli bacteria, which was detected on bean sprouts, has so far claimed 31 lives.

The Federal Institute for Risk Assessment in Berlin said yesterday that laboratory tests have shown a highly aggressive strain of E coli bacteria, which was detected on bean sprouts left over by two women in the state of North Rhine Westphalia and who fell ill after consuming the vegetable, was exactly identical with the strain found on bean sprouts in an organic farm in northern Germany.

According to the estimates of the Robert Koch Institute(RKI), more than 2,000 people have been infected with the bacteria and around 730 of them have the life-threatening haemolytic uramic syndrome (HUS), which can lead to acute kidney failures, strokes, seizures and coma.

It has been confirmed that bean sprouts were the main source of the outbreak and the farm in Bienenbuttel in the state of Lower Saxony was a breeding ground of the Escherichia coli bacteria, which has spread rapidly since the first case of infection was reported in Hamburg at the beginning of May, institute officials said.

For the first time since the outbreak of the E coli epidemic, scientists were able to establish a link between the farm in Bienenbuttel and patients infected with the bacteria, the Federal Ministry for Consumer Protection said.

Investigators are searching the entire distribution network of the farm to find out whether tainted bean sprouts are still in circulation and how the two women in a family near Bonn got the vegetable.

Investigations are also focusing on how the killer bacteria landed in the farm and whether three women workers, who became infected after eating bean sprouts, contributed to its spreading. Meanwhile, Germany's Federal Minister for Consumer Protection Ilse Aigner has called for more stringent control of imports, production and distribution of bean sprouts by state authorities.